Wasps create 'zombie' spiders to do their bidding, say scientists

By examining the parasitic relationship between ichneumon wasps and orb-weaving spiders, researchers hope to better understand chemical mind control in the animal world.

Let’s face it, parenting is hard work.

Maybe that’s why ichneumon wasps force spiders to house and feed their kids for them.

Through new research, scientists seek to understand the insidious mind control employed by Reclinervellus nielseni, a species of ichneumon wasp native to Japan. The larvae of R. nielseni latch onto orb-weaving spiders, forcing their hosts to spin special webs. When the web is finished, the zombified spiders wait patiently to be consumed by their wasp masters.

According to a study published Wednesday in the Journal of Experimental Biology, these wasps may only be enhancing the normal behavior of their hosts, not changing it outright.

Orb-weaving spiders can build two kinds of nests: complex webs designed to catch prey, and an interim “resting” webs that are weaved just before molting. Lead author Keizo Takasuka, a behavioral ecologist at Japan’s Kobe University, noticed that the webs built by zombie spiders looked an awful lot like their resting webs. But were the similarities a result of careful planning, or mere coincidence?

To find out, Dr. Takasuka and colleagues studied the web-building practices of both healthy and parasitized spiders. High-definition imaging showed no discernible difference between normal and zombie nests. But upon further investigation, researchers noticed that the latter were highly luminescent in ultraviolet light. This could prevent insects from accidentally careening into the larva’s safe space. These webs were also built tougher – up to 40 times more resistant to snapping than normal webs.

In other words, these parasite nests make the perfect rearing ground for young wasp larvae. It is still unclear exactly how this mechanism works, but Takasuka and colleagues propose one theory: by injecting them with hormone-like chemicals, the larvae could stimulate their host’s resting behavior. With just a few chemical adjustments, they could force spiders to strengthen the web or add a touch of bioluminescence.

“This discovery—of enhanced behavior as opposed to merely switched behavior—is completely new, impressively demonstrated, and rather unexpected I think,” Mark Shaw, an expert on ichneumon wasps at the National Museum of Scotland, told Newsweek.

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